Article

Role of the Clinical Mycobacteriology Laboratory in Diagnosis and Management of Tuberculosis in Low-Prevalence Settings

Johns Hopkins Medical Institutions, Baltimore, Maryland, Baltimore, Maryland, USA.
Journal of clinical microbiology (Impact Factor: 3.99). 12/2010; 49(3):772-6. DOI: 10.1128/JCM.02451-10
Source: PubMed
ABSTRACT
Tuberculosis (TB) remains a global epidemic, despite a significant decline in reported cases in the United States between 2008 and 2009. While the exact nature of this decline is unclear, one thing remains certain: TB, including multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB, is no longer restricted to developing regions of the globe. It is of vital importance that both public and private mycobacteriology laboratories maintain the ability to detect and identify Mycobacterium tuberculosis from patient specimens, as well as correctly determine the presence of antibiotic resistance. To do this effectively requires careful attention to preanalytical, analytical, and postanalytical aspects of testing. Respiratory specimens require digestion and concentration followed by fluorescence microscopy. The Centers for Disease Control and Prevention (CDC) recommends the performance of a direct nucleic acid amplification method, regardless of smear results, on specimens from patients in whom the suspicion of tuberculosis is high. Liquid-based technologies are more rapid and sensitive for the detection of M. tuberculosis in culture and nucleic acid probes, but biochemicals are preferred for identification once growth is detected. Susceptibility testing is most often done using either the agar proportion method or a commercial broth system. New genotypic and phenotypic methods of susceptibility testing include first- and second-line agents and are promising, though not yet widely available. Finally, gamma interferon release assays are preferred to the tuberculin skin test for screening certain at-risk populations, and new CDC guidelines are available that assist clinicians in their use.

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    • "Superimposed on this classic workflow (smear microscopy, culture, then DST), laboratories have overlaid molecular testing over the past two decades, using a variety of different platforms and clinical strategies. The first molecular tests approved were only licensed for the speciation of smear microscopy-positive samples [Parrish and Carroll, 2011], so their key role was in assigning a microbial name to such a sputum sample [Vuorinen et al. 1995; Carpentier et al. 1995]. Then, with time and experience, it became recognized that nucleic acid amplification testing could be offered on smear-negative samples where there was a high clinical suspicion of TB []. "
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    • "as well as Vadwai et al. (2011) have used smear, culture, histology/cytology, clinical findings and response to ATT, all together as the gold/reference standard for validating their PCR results in diagnosing EPTB specimens. There are several potential commercial kits devised to diagnose TB such as Amplicor M. tuberculosis test (Roche Molecular Systems Branchburg, NJ), Gen-probe Amplified M. tuberculosis Direct Test (AMTD; Gen-Probe, CA), COBAS TaqMan M. tuberculosis (Roche Molecular Systems Branchburg) and LightCycler (Roche Molecular Diagnostics, Mannheim, Germany; Ritis et al., 2005; Causse et al., 2011; Parrish & Carroll, 2011) Among these, Amplicor M. tuberculosis test and AMTD based on 16S rRNA gene have been approved by the US Food and Drug Administration (FDA) for the diagnosis of PTB only (Brodie & Schluger, 2009 ), and none of these commercial tests have been approved by FDA for the diagnosis of EPTB (Parrish & Carroll, 2011). However, the utility of these commercial tests has been extensively explored in the diagnosis of EPTB (Bouakline et al., 2003; Causse et al., 2011 ). "
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    • "The tubes were incubated for five and 12 days at 37ºC in an automated MGIT 960 device (Becton & Dickinson ). Readings were taken at hourly intervals during this period until the final growth index was attained in the growth control tube and a subsequent final report was issued (Kruuner et al. 2006, Rüsch-Gerdes et al. 2006, Parrish & Carroll 2011). Patients resistant to at least one antibiotic in the polychemotherapy regimen for TB were classified as monoresistant . "
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